This invention relates to typewriters and more particularly to print impression control mechanisms for typewriters, especially suitable for single element typewriters.
A single element typewriter having a single element printing head is conventionally provided with an impression control mechanism for regulating the impact velocity of the printing head against a platen to obtain a desired impression of characters printed on a record medium. In such a single element typewriter, a cyclically operable print drive cam is rendered operative in response to depression of any character key and drives a rocker platform to rock around an axis to fly the printing head on the rocker toward the platen. A cam follower transmits driving force of the print cam to the rocker thorugh a motion transmitting pin which is mounted on the rocker and is normally engaged with an arcuate cam section of the cam follower. An impression control lever is manually adjusted to position the motion transmitting pin relative to the arcuate cam section of the cam follower to thereby determine a distance over which the printing head is accelerated by the print cam, which will determine the impact velocity of the printing head against the platen in a well known manner. Such an impression control lever may be mounted on the rocker with the motion transmitting pin being fixed to an end of the lever, or else on a carrier with the cam follower being pivotally mounted on the lever as disclosed in U.S. Pat. No. 3,888,339.
Conventional single element typewriters usually accompany a problem that the printing element is normally located at a position relatively close to the platen so that printed characters on the record medium cannot be observed well by the operator of the typewriter. In a typewriter of the type provided with the above described impression control mechanism, the printing head is moved back and forth relative to the platen in response to manual adjustment of the impression control lever since the motion transmitting pin is normally engaged with the cam section of the cam follower. If the control lever is adjusted so that the possible lowest impression may be attained, the printing head in its rest position comes closest to the platen to provide a minimum spacing left therebetween so that an utmost influence is had on the eyesight of the machine operator. Adjustment of the control lever to a higher impression position would correspondingly widen the spacing between the printing element and the platen to thus improve the operator's eyesight.